1. Field of Invention
Embodiments of the invention relate generally to an apparatus for supporting a substrate in a semiconductor processing chamber.
2. Background of the Invention
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes. One fabrication process frequently used is chemical vapor deposition (CVD).
Chemical vapor deposition is generally employed to deposit a thin film on a substrate or semiconductor wafer. Chemical vapor deposition is generally performed in a vacuum chamber having a heated substrate support. The substrate is typically secured by vacuum to the heated substrate support to facilitate uniform temperature control across the surface of the substrate. A precursor gas is typically directed through a showerhead situated near the top of the chamber. The precursor gas reacts to form a layer of material on a surface of the substrate that is positioned on a heated substrate support. Purge gas is routed through holes in the support to the edge of the substrate to prevent deposition at the substrate""s edge or backside. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
One material frequently formed on substrates using a chemical vapor deposition process is tungsten. Precursor gases that may be used to form tungsten generally includes tungsten hexafluoride (WF6) and silane. As the silane and tungsten hexafluoride mix, some tungsten (i.e., tungsten that does not deposit on the substrate) deposits on the showerhead and other chamber components. The tungsten film that builds on the showerhead may become a source of contamination in the chamber. Eventually, the tungsten build-up may clog the holes in the showerhead that facilitate the passage of the precursor gas therethrough necessitating the showerhead be removed and cleaned or replaced.
To extend the interval in time between the routine maintenance of the showerhead, fluorine based chemistries are generally used to clean (i.e., etch away) the stray tungsten film. However, the use of fluorine, while advantageous for removing tungsten, reacts to form a layer of aluminum fluoride on the heated substrate support that is commonly made of aluminum. The aluminum fluoride layer has a generally rough surface topography. The rough surface creates a leak path that impairs the vacuum used to chuck or hold the substrate to the heated support. Additionally, the aluminum fluoride layer is a potential source of particulate contamination.
Substrate supports fabricated from ceramic materials provide an improvement over aluminum supports due to ceramic""s lack of reactivity with fluorine. However, ceramic supports are difficult to fabricate. For example, the holes in ceramic supports used to provide purge gas to the perimeter of the support are typically drilled from the perimeter of the support to a depth generally equal to the radius of the support. Drilling such a deep hole in ceramic is difficult. The tools used to make these holes are frequently broken during the fabrication (e.g., drilling) process. Broken tools disposed within the support must be removed or the support must be scrapped. These fabrication difficulties result in costly supports and an undesirable high scrap rate.
Alternatively, radial purge gas passages may be formed by sintering or fusing two ceramic plates to enclose the passages as described in the previously incorporated U.S. patent application Ser. No. 09/596,854. However, this technique results in a costly support as well.
Therefore, there is a need for an improved support for chemical vapor deposition processes.
One aspect of the present invention generally provides a substrate support assembly for supporting a substrate during processing. In one embodiment, a support assembly for supporting a substrate during processing includes a ceramic body having an embedded heating element and a base plate. The base plate and the ceramic body define a channel therebetween adapted to supply purge gas to a perimeter of the substrate disposed on the support assembly. The base plate is fastened to the body by brazing, adhering, fastening, press fitting or by mating engaging portions of a retention device such as a bayonet fitting.
In another embodiment, a support assembly includes a ceramic body having an embedded heating element coupled to a stem. A base plate is removably disposed adjacent the ceramic body and defines a channel therebetween adapted to supply purge gas to a perimeter of the substrate disposed on the support assembly.